Substantial technological growth has spurred a new interest in imaging techniques, and their usage has grown considerably. High-resolution small animal imaging systems have emerged as important new tools for laboratory animal research. X-ray imaging is widely used in diagnostic radiology, biomedical research and a wide variety of industrial applications. We propose to design and construct a portable, low cost micro-focus x-ray tube using the carbon nanotube (CNT) field emission source as the cathode to overcome disadvantages of the hot electron sources in the present x-ray tubes. By implementing the proposed research (Phase I and II), we expect to be able to demonstrate new compact x-ray tube with the following features: high imaging resolution down to 30 um or smaller, electronic controllable effective focal spot in 30 ~ 100 um range, portable device with extended lifetime of up to 3000 hours, capability of electronic triggering the x-ray at the rate of 1-10 millisecond (msec) per image, 100-500 uA tube current with 1% stability under 40-100KVp voltage. The primary application of the proposed x-ray source is for small animal imaging. The major research design and methods to achieve the proposed development goals include: a) Synthesis and processing of proprietary carbon nanotube materials; b) Fabrication of CNT based field emission cathode capable of generating 1-5 A/cm2 field emission current density, c) Integration of gated electron source employing the CNT source technique developed at Xintek, d) Evaluation of the electron emission characteristics including threshold field, current stability, and lifetime, e) Design and construction of prototype portable x-ray device, f) Computer simulation to the electron optics designed to simplify the focus structure, g) Evaluation of the new type x-ray tube by studying the key imaging characteristics: x-ray energy spectrum, flux, high voltage stability, spatial resolution/focal spot, pulsed x-ray radiation with millisecond pulse width.